1. Field of the Invention
The present invention relates to a method for producing a substrate for single crystal diamond growth.
2. Description of the Related Art
Diamond has a wide band gap of 5.47 eV and a very high dielectric breakdown electric field intensity of 10 MV/cm. Furthermore, it has the highest thermal conductivity in materials. Therefore, if this is used for an electronic device, the device is advantageous as a high output power device.
On the other hand, diamond has high drift mobility and is the most advantageous as a high-speed power device in semiconductors in comparison of Johnson performance index.
Accordingly, diamond is said to be the ultimate semiconductor suitable for high frequency/high power electronic devices.
Therefore, a multilayer substrate in which a diamond film and the like is laminated on a substrate has attracted attention.
Now, most of the single crystal diamonds for fabrication of a diamond semiconductor are diamonds referred to as Ib type formed by a high-pressure method. The Ib-type diamonds contain a large amount of nitrogen impurities and can only be obtained at a size of no more than about a 5-mm squar. Therefore, their utility is low.
By contrast, there is an advantage that by Chemical Vapor Deposition (CVD) method, a diamond of a relatively large area can be obtained with high purity.
Before growing a diamond film by this CVD method, a so-called bias treatment for forming a nucleus of diamond on a substrate before single crystal diamond growth by a direct-current discharge in which an electrode in a substrate side is a cathode has been performed.
For example, in Jpn. J. Appl. Phys. Vol. 35 (1996) pp. L1072-L1074 and NEW DIAMOND, Vol. 18 No. 4, (2002), pp. 6-12, a substrate for single crystal diamond growth has been produced by performing such a bias treatment at an Ir substrate temperature of 900° C. before the diamond growth. And, it has been reported that on the substrate, the diamond growth is performed by a DC plasma CVD method, and thereby a diamond grain having a uniform orientation can be grown.
Moreover, in 65th Japan Society of Applied Physics Academic Lecture Preliminary Report No. 2 (2004), pp. 508, it has been described that the bias treatment is performed at an Ir substrate temperature of 920° C. before the diamond growth, and it has been reported that the same result as the above-described Jpn. J. Appl. Phys. Vol. 35 (1996) pp. L1072-L1074 and NEW DIAMOND, Vol. 18 No. 4, (2002), pp. 6-12 can be obtained.
However, the above-described Jpn. J. Appl. Phys. Vol. 35 (1996) pp. L1072-L1074, NEW DIAMOND, Vol. 18 No. 4, (2002), pp. 6-12, and 65th Japan Society of Applied Physics Academic Lecture Preliminary Report No. 2 (2004), pp. 508 do not quite describe details about a method for measuring the temperature of the substrate, a condition thereof, a place for the measurement, and so forth. Furthermore, in experiments by the present inventor, even when any one of the other conditions complies with a condition described in the above-described Jpn. J. Appl. Phys. Vol. 35 (1996) pp. L1072-L1074 NEW DIAMOND, Vol. 18 No. 4, (2002), pp. 6-12, or 65th Japan Society of Applied Physics Academic Lecture Preliminary Report No. 2 (2004), pp. 508, it has been impossible to grow a single crystal diamond, on the substrate subjected to the bias treatment at approximately 900° C.